The present invention applies to the domain of electron-beam lithography. To allow the etching of patterns whose critical dimension is below 50 nm, it is necessary to integrate into the methods of optical photolithography schemes for correcting optical distortions that are increasingly complex both at the mask design and production stage and at the exposure stage. The costs of equipment and developments for a new generation of technology consequently increase in very high proportions. Today, the critical dimensions accessible in photolithography are greater than or equal to 65 nm. The 32-45 nm generation is undergoing development and there is no viable solution envisaged for technological nodes below 22 nm. For its part, electron-beam lithography already allows the etching of 22-nm patterns; it does not require any mask and offers a fairly short development time, thus allowing better reactivity and flexibility in the realization of improvements to the technologies and to the designs. On the other hand, the production times are structurally substantially higher than in photolithography since it is necessary to carry out step-by-step exposure, whereas photolithography requires only layer-wise exposure.
The electron beam or beams used to perform the etching of a pattern scatter notably over short distance (forward scattering or blur) in the resin and the substrate on the edges of the center of the beam, thus increasing the size of the beam and reducing its contrast. Moreover, the electrons are completely backscattered over a long distance (backward scattering). This proximity effect is particularly sensitive to the angles of the patterns to be etched or corners which are rounded. This effect reduces the precision of the etching, affects the functionality of the components and is liable to decrease integrated circuit production yields.
A certain number of prior art methods, in the domains of photolithography and electron-beam lithography, have attempted to make corrections to this phenomenon of corner rounding. Such is notably the case in photolithography of the methods providing for the modification of the patterns to be etched, notably by extension of their surface at the end of the line, such as those disclosed by K. Tsudaka et al., Japanese Journal of Applied Physics, Vol. 36 (1997), pp. 7477-7481, K. Kim et al., Japanese Journal of Applied Physics, Vol. 37 (1998), pp. 6681-6685 as well as by U.S. Pat. No. 7,494,751.
In electron-beam lithography, some methods are aimed at globally reducing the proximity effects, without addressing the specific problem of the rounding of the corners of the patterns to be etched. Such is notably the case for the scheme described in U.S. Pat. No. 6,107,207, which carries out a correction of the proximity effects by increasing the radiation doses at the pattern edge. This increase in dose is manifested by a new increase in the exposure times, thus constituting a very significant handicap for the industrial rollout of this technology.